[ubuntu] USB Harddrive versus USB keyboard.

I have a USB harddrive that mounts when booting except when I have a USB keyboard connected, if I disconnect the keyboard the drive mounts as usual.

I don’t understand why and what can I do to make sure that the USB harddrive is connected even if I have the keyboard (or any other USB devices attached)

This is normally not a problem as I use the computer as a headless ubuntu server, but if I connect usb devices to the computer I would like to be sure that the hardrive is mounted after a reboot.